AbstractThe unique ability of bats to act as reservoir for viruses that are highly pathogenic to humans suggests unique properties and functional characteristics of their immune system. However, the lack of bat specific reagents, in particular antibodies, has limited our knowledge of bat’s immunity. Using cross-reactive antibodies, we report the phenotypic and functional characterization of T cell subsets, B and NK cells in the fruit-eating bat Pteropus alecto. Our findings indicate the predominance of CD8⁺ T cells in the spleen from wild-caught bats that may reflect either the presence of viruses in this organ or predominance of this cell subset at steady state. Instead majority of T cells in circulation, lymph nodes and bone marrow (BM) were CD4⁺ subsets. Interestingly, 40% of spleen T cells expressed constitutively IL-17, IL-22 and TGF-β mRNA, which may indicate a strong bias towards the Th17 and regulatory T cell subsets. Furthermore, the unexpected high number of T cells in bats BM could suggest an important role in T cell development. Finally, mitogenic stimulation induced proliferation and production of effector molecules by bats immune cells. This work contributes to a better understanding of bat’s immunity, opening up new perspectives of therapeutic interventions for humans.